Add cache to FoldEscapingRegions

tests/ui/async-await/async-closures/post-mono-higher-ranked-hang-2.rs

@@ -0,0 +1,23 @@
+//@ edition: 2021
+//@ build-fail
+
+// Regression test for <https://github.com/rust-lang/rust/issues/135780>.
+
+use std::future::Future;
+use std::ops::AsyncFn;
+use std::pin::Pin;
+
+fn recur<'l>(closure: &'l impl AsyncFn()) -> Pin<Box<dyn Future<Output = ()> + 'l>> {
+    Box::pin(async move {
+        let _ = closure();
+        let _ = recur(&async || {
+            //~^ ERROR reached the recursion limit
+            let _ = closure();
+        });
+    })
+}
+
+fn main() {
+    let closure = async || {};
+    let _ = recur(&closure);
+}

tests/ui/async-await/async-closures/post-mono-higher-ranked-hang-2.stderr

@@ -0,0 +1,18 @@
+error: reached the recursion limit while instantiating `recur::<{async closure@$DIR/post-mono-higher-ranked-hang-2.rs:13:24: 13:32}>`
+  --> $DIR/post-mono-higher-ranked-hang-2.rs:13:17
+   |
+LL |           let _ = recur(&async || {
+   |  _________________^
+LL | |
+LL | |             let _ = closure();
+LL | |         });
+   | |__________^
+   |
+note: `recur` defined here
+  --> $DIR/post-mono-higher-ranked-hang-2.rs:10:1
+   |
+LL | fn recur<'l>(closure: &'l impl AsyncFn()) -> Pin<Box<dyn Future<Output = ()> + 'l>> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/async-await/async-closures/post-mono-higher-ranked-hang.rs

@@ -0,0 +1,63 @@
+//@ build-fail
+//@ aux-build:block-on.rs
+//@ edition:2021
+
+// Regression test for <https://github.com/rust-lang/rust/issues/135780>.
+
+extern crate block_on;
+
+use std::future::Future;
+use std::ops::AsyncFnMut;
+use std::pin::{Pin, pin};
+use std::task::*;
+
+trait Db {}
+
+impl Db for () {}
+
+struct Env<'db> {
+    db: &'db (),
+}
+
+#[derive(Debug)]
+enum SymPerm<'db> {
+    Dummy(&'db ()),
+    Apply(Box<SymPerm<'db>>, Box<SymPerm<'db>>),
+}
+
+pub struct ToChain<'env, 'db> {
+    db: &'db dyn crate::Db,
+    env: &'env Env<'db>,
+}
+
+impl<'env, 'db> ToChain<'env, 'db> {
+    fn perm_pairs<'l>(
+        &'l self,
+        perm: &'l SymPerm<'db>,
+        yield_chain: &'l mut impl AsyncFnMut(&SymPerm<'db>),
+    ) -> Pin<Box<dyn std::future::Future<Output = ()> + 'l>> {
+        Box::pin(async move {
+            match perm {
+                SymPerm::Dummy(_) => yield_chain(perm).await,
+                SymPerm::Apply(l, r) => {
+                    self.perm_pairs(l, &mut async move |left_pair| {
+                        //~^ ERROR reached the recursion limit while instantiating
+                        self.perm_pairs(r, yield_chain).await
+                    })
+                    .await
+                }
+            }
+        })
+    }
+}
+
+fn main() {
+    block_on::block_on(async {
+        let pair = SymPerm::Apply(Box::new(SymPerm::Dummy(&())), Box::new(SymPerm::Dummy(&())));
+        ToChain { db: &(), env: &Env { db: &() } }
+            .perm_pairs(&pair, &mut async |p| {
+                eprintln!("{p:?}");
+            })
+            .await;
+    });
+}

tests/ui/async-await/async-closures/post-mono-higher-ranked-hang.stderr

@@ -0,0 +1,21 @@
+error: reached the recursion limit while instantiating `ToChain::<'_, '_>::perm_pairs::<{async closure@$DIR/post-mono-higher-ranked-hang.rs:43:45: 43:67}>`
+  --> $DIR/post-mono-higher-ranked-hang.rs:43:21
+   |
+LL | /                     self.perm_pairs(l, &mut async move |left_pair| {
+LL | |
+LL | |                         self.perm_pairs(r, yield_chain).await
+LL | |                     })
+   | |______________________^
+   |
+note: `ToChain::<'env, 'db>::perm_pairs` defined here
+  --> $DIR/post-mono-higher-ranked-hang.rs:34:5
+   |
+LL | /     fn perm_pairs<'l>(
+LL | |         &'l self,
+LL | |         perm: &'l SymPerm<'db>,
+LL | |         yield_chain: &'l mut impl AsyncFnMut(&SymPerm<'db>),
+LL | |     ) -> Pin<Box<dyn std::future::Future<Output = ()> + 'l>> {
+   | |____________________________________________________________^
+
+error: aborting due to 1 previous error
+